Les matériaux ferroélectriques présentant une permittivité diélectrique élevée et de faibles pertes diélectriques présentent un grand intérêt pour la réalisation de condensateurs et le stockage de l'énergie électrique. Les propriétés structurales et diélectriques influencent les paramètres ferroélectriques tels que la polarisation maximale du matériau Pm et la polarisation rémanente Pr sous l'effet d'un champ électrique appliqué Em. Ce mémoire propose d'étudier les propriétés structurales, diélectriques et ferroélectriques des céramiques dérivées de BaTiO₃ (BT) et SrTiO₃ (ST) ainsi que des films épais PVDF pur et composites tels que PVDF/BT et PVDF/BZT. Les céramiques ont été synthétisées par la méthode de la réaction solide et le procédé sol-gel. La substitution dans les sites-A ou les sites-B du matériau BaTiO₃ avec des cations tels que Ca ²⁺, Sr²⁺ and Zr⁴⁺ réduit la densité d'énergie électrique stockée Wd et augmente l'efficacité de stockage énergétique η. La céramique BaZr₀.₅Ti₀.₅O₃ (BZT0.5) présente l'efficacité de stockage énergétique la plus élevée (η=75%). La substitution dans les sites-A du matériau SrTiO₃ avec 40% de cations Ca²⁺ diminue la permittivité diélectrique (ε'∽200), mais cette permittivité est cependant plus stable sur une large gamme de fréquence [100 Hz-1 GHz]. La céramique Sr₀.₆Ca₀.₄TiO₃ préparée par voie sol-gel présente la densité d'énergie électrique stockée la plus élevée (Wd=0.149 J/cm³) sous l'action d'un champ électrique maximal élevé (Em=105 kV/cm). Les films épais à base de polymère PVDF ont été synthétisés par Spin-Coating. La permittivité diélectrique des films épais PVDF pur augmente avec l'apaisseur du film. L'incorporation de particules BT et BZT0.15 dans la matrice polymère PVDF augmente la permittivité diélectrique des films composites PVDF/BT (ε'=32 pour 30% de particules BT) et PVDF/BZT0.15 (ε'=32 pour15% de particules BZT). / Ferroelectric materials with a high dielectric permittivity and low dielectric losses are very attractive for the realization of capacitors and for electrical energy storage. To improve the electrical energy density Wd, the structural and dielectric properties influence the ferroelectric parameters such as the maximum polarization Pm and the remanent polarization Pr under an applied electric field Em. This manuscript proposes to study the structural, dielectric and ferroelectric properties of ceramics derived from BaTiO₃ (BT) and SrTiO₃ (ST) as well as pure PVDF thick films and composites such as PVDF/BT and PVDF/BZT. The ceramics were synthesized by the solid state reaction reaction route and the sol-gel process. The subsitution in the A-sites or B-sites of the BaTiO₃ material with cations such Ca²⁺, Sr²⁺ and Zr⁴⁺ reduces the electrical energy density Wd and increases the energy storage efficiency η. The ceramic BaZr₀.₅Ti₀.₅O₃ (BZT0.5) has the highest energy storage efficiency (η=75%). The substitution in the A-sites of SrTiO₃ material with 40% of Ca²⁺ cations reduces the dielectric permittivity (ε'∽200), but is more stable over a wide frequency range [100 Hz -1 GHZ]. The Sr₀.₆Ca₀.₄TiO₃ ceramic prepared by sol-gel process has the highest electrical energy density (Wd = 0.149 J/cm³) under an electrical field Em = 105 kV/cm. The PVDF thick films were synthesized by Spin-Coating. The dielectric permittivity of pure PVDF thick films increases when increasing the thickness. The addition of BT and BTZ0.15 particles in the PVDF polymer matrix increases the dielectric permittivity of the composite PVDF/BT thick films (ε'=32 for 30% of BT particles) and PVDF/BZT0.15 ones (ε'=32 for 15% of BZT particles).

Orientador: Andrea Carvalho De Marco / Coorientador: Dimas Renó de Lima / Banca: Symone Cristina Teixeira / Banca: Cibelle Barbosa Lopes / Resumo: A hipersensibilidade dentinária é uma das complicações mais comuns entre os pacientes após o tratamento periodontal. Recentemente a terapia com o uso de laser de baixa intensidade foi introduzida como uma nova modalidade de tratamento e tem proporcionado resultados benéficos. Foi realizado um estudo clínico controlado, randômico, duplo-cego, de boca dividida com o objetivo de comparar a efetividade do uso do verniz tópico Fluoreto de sódio 5%, do Laser GaAlAs 780 nm e da combinação do Fluoreto de sódio 5% e o Laser GaAlAs 780 nm para o tratamento de hipersensibilidade dentinária. Os Grupos foram divididos em Grupo Controle (C), Grupo Fluoreto de sódio 5% (F), Grupo Laser GaAlAs 780 nm (LLLT), e o Grupo Fluoreto de sódio 5% + Laser GaAlAs 780 nm (F+LLLT). A aplicação do verniz foi realizada com pinceis do tipo "microbrush", e para cada elemento dental cinco pontos receberam a LLLT, com dose de 52,5 J/cm2 (70mW e 30 segundos) ou 2,1 J por ponto; 6 segundos por ponto. A hipersensibilidade primária foi registrada pela escala analógica visual (VAS: 0-10) para quantificar a dor subjetiva após estímulo com "spray de gelo" no baseline, e após o tratamento nos intervalos de 24 horas e 30 dias. Todos os dados foram analisados estatisticamente pela análise de variância ANOVA. Para cada um dos três tempos de avaliação foi efetuada uma comparação entre os 4 grupos (por meio da ANOVA oneway) com complementação pelos testes de Tukey e Bartlett a fim de verificar as diferenças estatísticas e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Dentin hypersensitivity is one of the most common complications among patients after periodontal treatment. Recently the low level laser therapy has been introduced as a new treatment modality and has provided beneficial results. A split-mout, double-blind, randomized, controlled clinical trial was conducted with the aim of compare the effectiveness of the topical varnish 5% Sodium Fluoride, Laser GaAlAs 780 nm and the combination of 5% Sodium Fluoride and the Laser GaAlAs 780 nm for the treatment of dentin hipersensitivity. The groups were divided in Control Group (C), Sodium Fluoride at 5% Group (F), Laser Group GaAlAs 780 nm (LLLT), and Sodium Fluoride at 5% Group + GaAlAs Laser 780 nm (F + LLLT). The application of the varnish was realized with "microbrush", and for each dental element, five points was received LLLT. The dose was 52.5 J / cm2 (70mW and 30 seconds) or 2.1 J per point, 6 seconds per point. Primary hypersensitivity was be recorded by visual analogue scale (VAS: 0-10) to quantify subjective pain after the stimulus with "ice spray" at baseline, and after treatment at 24-hour and 30-day intervals. All data was analyzed statistically by analysis of variance ANOVA. For each of the three evaluation times a comparison was made between the 4 groups (through the oneway ANOVA) with complementation by the Tukey's and Bartlett's tests in order to verify the statistical differences between groups. The level of significance will be 5%. After statistical analysis the resul... (Complete abstract click electronic access below) / Mestre

Die feste nichtkristalline Lewis-Säure Aluminiumchlorofluorid (ACF, AlCl(x)F(3-x), x = 0.05 .. 0.3) hat die höchste bisher bekannte Lewis-Acidität aller heterogenen Katalysatoren. Sie erreicht die Stärke von Antimonpentafluorid SbF5 und übertrifft sie in manchen Fällen sogar. In dieser Arbeit wurden die Bulk-Struktur des ACF und der sehr ähnlichen Verbindung Aluminiumbromofluorid (ABF) mittels IR-, ESR-, NMR- und Röntgenabsorptionsspektroskopie studiert. Die Oberfläche der Verbindungen wurde durch die Adsorption von Gasen bei niedrigen Temperaturen untersucht, sowie durch IR- und ESR-Spektroskopie adsorbierter Sondenmoleküle. Das thermische Verhalten dieser nichtkristallinen Verbindungen wurde mittels DTA verfolgt. Die Lewis-Acidität kleiner Modellverbindungen wurde NMR-spektroskopisch und mit ab initio Methoden untersucht. Alle Daten wurden mit denen der gut charakterisierten und bekannten Modifikationen des Aluminiumfluorids (AlF3) verglichen. Die kombinierten Ergebnisse der Messungen an beiden festen Phasen erlauben die Entwicklung eines Strukturmodells für diese Verbindungen, das die meisten spektroskopischen Daten und die außergewöhnlich hohe Lewis-Acidität erklären kann. Beide Phasen sind sehr ähnlich zueinander. Das Vorhandensein des schwereren Halogens (Cl, Br) erzeugt eine Störung des Netzwerkes und verhindert die Ausbildung geordneter Strukturen. Der Grad der Unordnung in diesen Phasen ist höher als bei allen anderen Verbindungen des Aluminiumfluorids. Daraus resultiert eine gestörte Oberfläche, was wiederum zu koordinativ ungesättigtem Aluminium an der Oberfläche führt. Die sauren Zentren in ACF und ABF sind stärker als in anderen aluminiumhaltigen Lewis-Säuren. / The solid non-crystalline Lewis acid aluminum chlorofluoride (ACF, AlCl(x)F(3-x), x = 0.05 .. 0.3) has the highest Lewis acidity of any heterogeneous catalyst known so far. It reaches the acidity of antimony pentafluoride (SbF5) and in some cases even exceeds it. In this work the bulk structure of ACF and of the very similar compound aluminium bromofluoride (ABF) was studied by IR, ESR, NMR, and X-ray absorption spectroscopy. The surface of the compounds was investigated by adsorption of gases at low temperatures, as well as by IR and ESR spectroscopy of adsorbed probe molecules. The thermal behavior of these non-crystalline compounds was followed by DTA. The Lewis acidity of small model compounds was studied by NMR spectroscopy and ab initio calculations. All data were compared to those of well characterized known samples of the different modifications of aluminum fluoride (AlF3). The combined results of the measurements of both solid phases allow to set up a structure model for these compounds which can explain most of the spectrocopic data and the extraordinary high Lewis acidity. Both phases are very similar to each other. The occurrence of the heavier halogen (Cl, Br) causes a perturbation of the network and prevents it from forming ordered structures. The degree of disorder of these phases is higher than for any other known compounds of aluminum fluoride. This results in an disordered surface which leads to coordinatively unsaturated aluminum at the surface. The acidic centers of ACF and ABF are stronger than in any other aluminum containing Lewis acid.

Magnetism of carbon-based materials is a challenging area for both fundamental research and possible applications. We present studies of low-dimensional carbon-based magnetic systems (fullerene-diluted molecular magnets, carbon nanotubes, graphite fluoride, and nanoporous carbon) by means of SQUID magnetometer, X-ray diffraction and vibrational spectroscopy, the latter techniques used as complementary instruments to find a correlation between the magnetic behaviour and the structure of the samples.In the first part of the thesis, characteristic features of the magnetization process in aligned films of carbon nanotubes with low concentration of iron are discussed. It is shown that the magnetism of such structures is influenced by quantum effects, and the anisotropy behaviour is opposite to what is observed in heavily doped nanotubes.In the second part, Mn12-based single molecular magnets with various carboxylic ligands and their 1:1 fullerene-diluted complexes are studied. We prove that magnetic properties of such systems strongly depend on the environment, and, in principle, it is possible to design a magnet with desirable properties. One of the studied compounds demonstrated a record blocking temperature for a single molecular magnet. Both fullerene-diluted complexes demonstrated “magnetization training” effect in alternating magnetic fields and the ability to preserve magnetic moment.The third and the fourth parts of the thesis are dedicated to the analysis of various contributions to the magnetic susceptibility of metal-free carbon-based systems – intercalated compounds of graphite fluorides and nanoporous oxygen-eroded graphite. The magnetic properties of these systems are strongly dependent on structure, and can be delicately tuned by altering the π-electron system of graphite, i. e. by degree of fluorination of intercalated compounds and by introduction of boron impurity to the host matrix of nanoporous graphite. / Magnetism av kolbaserade material är ett utmanande område för både grundforskning och möjliga tillämpningar. Vi presenterar studier med låg-dimensionella kolbaserade magnetiska system (fulleren-utspädda molekylära magneter, kolnanorör, grafit fluorid och nanoporösa kol) med hjälp av SQUID magnetometer, röntgendiffraktion och vibrerande spektroskopi, de senare tekniker som används som komplement instrument för att finna sambandet mellan den magnetiska uppträdande och strukturen hos proven. I den första delen av avhandlingen är egenheter från magnetisering processen i linje filmer av kolnanorör med låg koncentration av järn diskuteras. Det visas att magnetism av sådana strukturer påverkas av kvantmekaniska effekter och anisotropin beteende är motsatsen till vad som observerats i kraftigt dopade nanorör. I den tvåa delen är Mn12-baserade enda-molekyl magneter med olika karboxylsyror ligander och deras 1:1 fulleren-utspädda komplex studeras. Vi visar att magnetiska egenskaperna hos sådana system beror i hög grad på miljön, och i princip är det möjligt att utforma en magnet med önskvärda egenskaper. En av de studerade föreningarna visade en post blockeringstemperaturen för en enda molekylär magnet. Både fulleren-utspädda komplex visade "magnetisering utbildning" effekt i alternerande magnetfält och möjligheten att bevara magnetiskt moment. Den tredje och fjärde delarna av avhandlingen är avsedda för inneboende magnetism av analys av olika bidrag till magnetisk susceptibilitet av metall-fritt kol-baserade system -inskjutna föreningar grafit fluorider och nanoporösa O2-eroderade grafit. Magnetiska egenskaperna hos dessa system är starkt beroende av strukturen, och kan fint avstämmas genom att man ändrar π-elektronsystem av grafit, i. e. med graden av fluorering av inskjutna föreningar och genom införandet av bor föroreningar till värd matris av nanoporösa grafit.

Cycling of the relative humidity (RH) levels in the reactant streams of polymer electrolyte membrane (PEM) fuel cells has been reported to decay fuel cell performance. This study focuses on the accelerated durability testing to examine different modes of membrane failure via RH cycling. A single PEM fuel cell with an active area of 42.25 cm2 was tested. A Greenlight G50 test station was used to establish baseline cell (Run 1) performance with 840 hours of degradation under high-humidity idle conditions at a constant current density of 10 mA cm-2. Under the same conditions, two other experiments were conducted by varying the RH. For the H2-air RH cycling test (Run 2), anode and cathode inlet gases were provided as dry and humidified gases. Another RH cycling experiment was the H2 RH cycling test (Run 3): the anode inlet gas was cycled whereas keeping the other side constantly at full humidification. These two RH cycling experiments were alternated in dry and 100% humidified conditions every 10 and 40 minutes, respectively. In the experiments, the fuel cells contained a GoreTM 57 catalyst coated membrane (CCM) and 35 BC SGL gas diffusion layers (GDLs). The fuel cell test station had been performed under idle conditions at a constant current density of 10 mA cm-2. Under the idle conditions, operating at very low current density, a low chemical degradation rate and minimal electrical load stress were anticipated. However, the membrane was expected to degrade due to additional stress from the membrane swelling/contraction cycle controlled by the RH. In this work the performance of the 100% RH humidified cell (Run 1) was compared with that of RH cycling cells (Run 2 and Run 3). Chemical and mechanical degradation of the membrane were investigated using in-situ and ex-situ diagnostic methods. The results of each measurement during and after fuel cell operation are consistent. They clearly show that changing in RH lead to an overall PEM fuel cell degradation due to the increase in membrane degradation rate from membrane resistance, fluoride ion release concentration, hydrogen crossover current, membrane thinning, and hot-spot/pin-hole formation.

Höchste Magnetfelder haben sich zu einem unverzichtbaren Werkzeug der Festkörperphysik entwickelt. Sie werden insbesondere verwendet, um die elektronischen Eigenschaften von modernen Materialien zu erforschen. Da Magnetfelder oberhalb von 45 Tesla nicht mehr mit statischen (z.B. supraleitenden) Feldern zu erreichen sind, haben sich weltweit verschiedene Labore auf die Erzeugung gepulster Magnetfelder mit angestrebten Maximalwerten von 100 Tesla spezialisiert. In der vorliegenden Arbeit werden Anwendungsmöglichkeiten der kernmagnetischen Resonanz (NMR) in gepulsten Magnetfeldern aufgezeigt. Es ist gelungen, die starke Zeitabhängigkeit der gepulsten Magnetfelder mittels NMR präzise zu vermessen. Die genaue Kenntnis des Magnetfelds nach dem Puls ermöglicht, die Zeitabhängigkeit aus den Daten zu entfernen, sodass auch eine kohärente Signal-Mittelung möglich ist. Davon ausgehend werden erstmalig Messungen der chemischen Verschiebung, der Knight Shift, der Spin-Gitter-Relaxationsrate 1/T1 und der Spin-Spin-Relaxationsrate 1/T2 diskutiert. Schließlich werden die im Zusammenhang mit gepulsten Magnetfeldern erarbeiteten Gleichungen in vereinfachter Form zur genauen Messung und Analyse des freien Induktions-Zerfalls von 19F Kernspins in Calciumfluorid verwendet. Durch Messung des Zerfalls über sechs Größenordnungen wird eine genaue Analyse bezüglich einer neuartigen Theorie ermöglicht, welche den Zerfall basierend auf der Annahme mikroskopischen Chaos\' erklärt. Diese Theorie hat das Potenzial, zu einem tieferen Verständnis von Quantenchaos in makroskopischen Vielteilchensystemen zu führen.

No description available.

Hydrogen is currently considered by many as the “fuel of the future”. It is particularly favoured as a replacement for fossil fuels due to its clean-burning properties; the waste product of combustion being water. While hydrogen is relatively easy to produce, there is currently a lack of practical storage methods for molecular H2, and this is greatly hindering the use of hydrogen as a fuel. Gases are normally stored in vessels under only moderate pressures and in liquid form where possible, which yields the highest energy density. However, to store reasonable quantities of hydrogen in similar volume containers, cryogenic temperatures or extreme pressure are required. Many potential hydrogen storage technologies are currently under investigation, including adsorption on metal hydrides, nanotubes and glass microspheres, and the chemical breakdown of compounds containing hydrogen to release H2. Recent studies have sparked interest in hydrates as a potential hydrogen storage material. The molecular storage of hydrogen in clathrate hydrates could offer significant benefits with regard to ease of formation/regeneration, cost and safety, as compared to other storage materials currently under investigation. Here, we present new experimental hydrate stability data for sII forming hydrogen–water (up to pressures of 180 MPa) and hydrogen–water–tetrahydrofuran systems, the structure-H forming hydrogen–water–methyclycohexane system, and semi-clathrate forming hydrogen–water–tetra-n-butyl ammonium bromide/tetra–n-butyl ammonium fluoride systems.

The use of small molecule building blocks in, for example, pharmaceutical research and new material development, creates a need for new and improved organic synthesis methods. The use of transition metals as mediators and catalysts opens up new reaction pathways that have made the synthesis of completely new compounds possible as well as greatly improved the synthetic routes to known compounds. Herein, the development of new metal-mediated and catalyzed reactions for construction of vinylic and allylic carbon-carbon and carbon-heteroatom bonds is described.  The use of iodonium salts as coupling partners in Pd-catalyzed Heck type reactions with alkenes is shown to improve the current substrate scope. Results from a mechanistic study indicate that the reaction proceeds via high oxidation state palladium intermediates. The use of IIII reagents is also believed to facilitate a PdII/PdIV catalytic cycle in allylic silylation of alkenes using (SiMe3)2, which, to the best of our knowledge, is the first method developed for metal-catalyzed allylic C-H silylation. The same silyl-source, (SiMe3)2, has previously been used in a Pd-catalyzed allylic substitution reaction in which allylic silanes are formed from allylic alcohols. A detailed mechanistic investigation of this reaction is described in which by-products as well as intermediates, including the resting state of the catalyst, are identified using 1H, 11B, 19F and 29Si NMR spectroscopy. Kinetic experiments are performed that give information about the turn-over limiting step and the mechanism of the analogous borylation using B2pin2 is also investigated. Insights from this study further made it possible to improve the stereoselectivity of this reaction. Additionally, a new method for Cu-mediated trifluoromethylation of allylic halides is presented in which linear products are formed exclusively from both linear and branched allylic substrates at room temperature.  Identification of allylic fluorides as by-products during the reaction also led to the development of a similar Cu-mediated reaction for the fluorination of allylic halides. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Objectif : il a été rapporté que l’utilisation d’agents prophylactiques fluorés pouvait favoriser la corrosion galvanique au sein des alliages de titane. L’objectif de la présente étude était d’évaluer l’effet d’un rince-bouche fluoré sur les propriétés mécaniques de fils en nickel-titane (NiTi) et de fils en cuivre-nickel-titane (CuNiTi) lorsque ces derniers sont couplés à des boîtiers de compositions différentes (boîtiers de marques Smartclip, Clarity, et Sprint). Matériels et Méthodes : 90 segments de fils en NiTi et 90 segments de fils en CuNiTi ont été chacun couplés à 2 boîtiers de chaque marque. Chaque assemblage fil-boîtiers a été par la suite incubé pendant 3 heures à 37°C, soit dans une solution de fluore neutre (Fluorinse™ 0,05% NaF), soit dans une solution de salive artificielle (solution contrôle). Suite à l’incubation, les échantillons étaient nettoyés avec de l’eau déshydrogénée, les fils séparés des boîtiers et montés sur un support pour subir un test de pliage en trois points en milieu humide (salive artificielle) à 37°C. Les modules d’élasticité ainsi que les limites conventionnelles d’élasticité en activation et en désactivation ont été mesurés et comparés. Des analyses de Variance (ANOVA) et des comparaisons post-hoc avec la correction de Bonferronni ont été utilisées pour comparer les groupes entre eux (α = 0,05). Résultats : L’utilisation d’un rince-bouche fluoré a produit une réduction du module d’élasticité et de la limite conventionnelle d’élasticité en activation et en désactivation pour les fils en NiTi ; cependant, cet effet a été modulé par le type de boîtier auquel le fil a été couplé. Les propriétés mécaniques de fils en CuNiTi n’ont pas été affectées par le fluor, ou par le type de boîtier utilisé. Conclusions : L’utilisation d’un rince-bouche fluoré modifie les propriétés mécaniques des fils en NiTi seulement. Cet effet est modulé par le boîtier auquel le fil en NiTi est couplé. A la différence des autres études publiées dans la littérature, nos résultats ne nous permettent pas de conclure que la modification des propriétés mécaniques des fils en NiTi entrainerait obligatoirement un allongement de la durée du traitement orthodontique. Mots clés : Fluor, fils nickel-titane, boîtiers orthodontiques, corrosion galvanique, propriétés mécaniques. / Aim: it has been reported that the use of fluoride prophylactic agents can cause galvanic corrosion of the titanium based alloys used in orthodontics. The purpose of the present study was to investigate the effects of a fluoride mouthrinse on the mechanical properties of nickel-titanium (NiTi) and copper–nickel-titanium (CuNiTi) orthodontic archwires that have been coupled with different types of orthodontic brackets (Smartclip, Clarity, and Sprint brackets). Materials and Methods: 90 segments of NiTi and 90 segments of CuNiTi archwires were tested. Every segment was coupled with 2 brackets of each brand. The wire–bracket assembly obtained was incubated, at 37°C for three hours either in a solution of a commercially available mouthwash (Fluorinse™ 0,05% NaF), or in a solution of artificial saliva (control). Following the incubation, the wires were separated from the brackets, rinsed, mounted on a stainless steel support and placed in a waterbath of artificial saliva at 37°C. A 3-point bending test was made to calculate the loading and unloading elastic modulus and yield strength of the wires. Analysis of variance (ANOVA) and post hoc comparisons were made using Bonferronni’s correction to identify the statistically significant differences (α = 0,05). Results: The use of a fluoridated mouthrinse reduced the loading and unloading elastic modulus and yield strength of the NiTi wires. This reduction, however, varies with the type of bracket that was coupled with the wire. The mechanical properties of the CuNiTi wires were not modified by the use of the fluoride rinse or by the type of bracket to which they were coupled. Conclusions : The use of a fluoride mouthrinse alters the mechanical properties of NiTi wires only. This effect varies with the type of bracket that was in contact with the wire. However our results do not allow us to conclude that the alteration of the mechanical properties of the wires would necessarily imply a prolongation of the orthodontic treatment time. Key words: Fluoride, nickel-titanium archwires, galvanic corrosion, mechanical properties,orthodontic brackets.